matplotlib中换行的文本框？

Question

是否可以通过 Matplotlib 在框中显示文本，自动换行？通过使用pyplot.text()，我只能打印超出窗口边界的多行文本，这很烦人。事先不知道线条的大小......任何想法将不胜感激！

Answer 1

此答案的内容已合并到 https://github.com/matplotlib/matplotlib/pull/4342 的 mpl master 中，并将在下一个功能版本中。

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哇...这是一个棘手的问题...（并且它暴露了matplotlib的文本渲染中的很多限制...）

这应该（i.m.o.）是 matplotlib 内置的东西，但事实并非如此。邮件列表中有几个threads about it，但我找不到自动换行的解决方案。

因此，首先，在 matplotlib 中绘制之前，无法确定渲染文本字符串的大小（以像素为单位）。这不是太大的问题，因为我们可以绘制它，获取大小，然后重新绘制包装的文本。 （虽然很贵，但也不算太差）

下一个问题是字符没有以像素为单位的固定宽度，因此将文本字符串包装到给定数量的字符不一定会在渲染时反映给定的宽度。不过，这不是一个大问题。

除此之外，我们不能只做一次......否则，它会在第一次绘制时正确包裹（例如在屏幕上），但如果再次绘制（当图形调整大小或保存为与屏幕具有不同 DPI 的图像）。这不是一个大问题，因为我们可以将回调函数连接到 matplotlib 绘制事件。

无论如何，这个解决方案是不完美的，但它应该适用于大多数情况。我不会尝试考虑 tex 渲染的字符串、任何拉伸字体或具有不寻常纵横比的字体。但是，它现在应该可以正确处理旋转的文本。

但是，它应该尝试自动将任何文本对象包装在多个子图中，无论您将on_draw 回调连接到哪个图形...它在许多情况下都是不完美的，但它做得不错。

import matplotlib.pyplot as plt

def main():
    fig = plt.figure()
    plt.axis([0, 10, 0, 10])

    t = "This is a really long string that I'd rather have wrapped so that it"\
    " doesn't go outside of the figure, but if it's long enough it will go"\
    " off the top or bottom!"
    plt.text(4, 1, t, ha='left', rotation=15)
    plt.text(5, 3.5, t, ha='right', rotation=-15)
    plt.text(5, 10, t, fontsize=18, ha='center', va='top')
    plt.text(3, 0, t, family='serif', style='italic', ha='right')
    plt.title("This is a really long title that I want to have wrapped so it"\
             " does not go outside the figure boundaries", ha='center')

    # Now make the text auto-wrap...
    fig.canvas.mpl_connect('draw_event', on_draw)
    plt.show()

def on_draw(event):
    """Auto-wraps all text objects in a figure at draw-time"""
    import matplotlib as mpl
    fig = event.canvas.figure

    # Cycle through all artists in all the axes in the figure
    for ax in fig.axes:
        for artist in ax.get_children():
            # If it's a text artist, wrap it...
            if isinstance(artist, mpl.text.Text):
                autowrap_text(artist, event.renderer)

    # Temporarily disconnect any callbacks to the draw event...
    # (To avoid recursion)
    func_handles = fig.canvas.callbacks.callbacks[event.name]
    fig.canvas.callbacks.callbacks[event.name] = {}
    # Re-draw the figure..
    fig.canvas.draw()
    # Reset the draw event callbacks
    fig.canvas.callbacks.callbacks[event.name] = func_handles

def autowrap_text(textobj, renderer):
    """Wraps the given matplotlib text object so that it exceed the boundaries
    of the axis it is plotted in."""
    import textwrap
    # Get the starting position of the text in pixels...
    x0, y0 = textobj.get_transform().transform(textobj.get_position())
    # Get the extents of the current axis in pixels...
    clip = textobj.get_axes().get_window_extent()
    # Set the text to rotate about the left edge (doesn't make sense otherwise)
    textobj.set_rotation_mode('anchor')

    # Get the amount of space in the direction of rotation to the left and 
    # right of x0, y0 (left and right are relative to the rotation, as well)
    rotation = textobj.get_rotation()
    right_space = min_dist_inside((x0, y0), rotation, clip)
    left_space = min_dist_inside((x0, y0), rotation - 180, clip)

    # Use either the left or right distance depending on the horiz alignment.
    alignment = textobj.get_horizontalalignment()
    if alignment is 'left':
        new_width = right_space 
    elif alignment is 'right':
        new_width = left_space
    else:
        new_width = 2 * min(left_space, right_space)

    # Estimate the width of the new size in characters...
    aspect_ratio = 0.5 # This varies with the font!! 
    fontsize = textobj.get_size()
    pixels_per_char = aspect_ratio * renderer.points_to_pixels(fontsize)

    # If wrap_width is < 1, just make it 1 character
    wrap_width = max(1, new_width // pixels_per_char)
    try:
        wrapped_text = textwrap.fill(textobj.get_text(), wrap_width)
    except TypeError:
        # This appears to be a single word
        wrapped_text = textobj.get_text()
    textobj.set_text(wrapped_text)

def min_dist_inside(point, rotation, box):
    """Gets the space in a given direction from "point" to the boundaries of
    "box" (where box is an object with x0, y0, x1, & y1 attributes, point is a
    tuple of x,y, and rotation is the angle in degrees)"""
    from math import sin, cos, radians
    x0, y0 = point
    rotation = radians(rotation)
    distances = []
    threshold = 0.0001 
    if cos(rotation) > threshold: 
        # Intersects the right axis
        distances.append((box.x1 - x0) / cos(rotation))
    if cos(rotation) < -threshold: 
        # Intersects the left axis
        distances.append((box.x0 - x0) / cos(rotation))
    if sin(rotation) > threshold: 
        # Intersects the top axis
        distances.append((box.y1 - y0) / sin(rotation))
    if sin(rotation) < -threshold: 
        # Intersects the bottom axis
        distances.append((box.y0 - y0) / sin(rotation))
    return min(distances)

if __name__ == '__main__':
    main()

Answer 2

大约五年过去了，但似乎仍然没有一个很好的方法来做到这一点。这是我接受的解决方案的版本。我的目标是允许将像素完美的包装选择性地应用于单个文本实例。我还创建了一个简单的 textBox() 函数，它将任何轴转换为具有自定义边距和对齐方式的文本框。

我没有假设特定的字体纵横比或平均宽度，而是一次绘制一个单词并在达到阈值时插入换行符。与近似值相比，这速度非常慢，但对于

# Text Wrapping
# Defines wrapText which will attach an event to a given mpl.text object,
# wrapping it within the parent axes object.  Also defines a the convenience
# function textBox() which effectively converts an axes to a text box.
def wrapText(text, margin=4):
    """ Attaches an on-draw event to a given mpl.text object which will
        automatically wrap its string wthin the parent axes object.

        The margin argument controls the gap between the text and axes frame
        in points.
    """
    ax = text.get_axes()
    margin = margin / 72 * ax.figure.get_dpi()

    def _wrap(event):
        """Wraps text within its parent axes."""
        def _width(s):
            """Gets the length of a string in pixels."""
            text.set_text(s)
            return text.get_window_extent().width

        # Find available space
        clip = ax.get_window_extent()
        x0, y0 = text.get_transform().transform(text.get_position())
        if text.get_horizontalalignment() == 'left':
            width = clip.x1 - x0 - margin
        elif text.get_horizontalalignment() == 'right':
            width = x0 - clip.x0 - margin
        else:
            width = (min(clip.x1 - x0, x0 - clip.x0) - margin) * 2

        # Wrap the text string
        words = [''] + _splitText(text.get_text())[::-1]
        wrapped = []

        line = words.pop()
        while words:
            line = line if line else words.pop()
            lastLine = line

            while _width(line) <= width:
                if words:
                    lastLine = line
                    line += words.pop()
                    # Add in any whitespace since it will not affect redraw width
                    while words and (words[-1].strip() == ''):
                        line += words.pop()
                else:
                    lastLine = line
                    break

            wrapped.append(lastLine)
            line = line[len(lastLine):]
            if not words and line:
                wrapped.append(line)

        text.set_text('\n'.join(wrapped))

        # Draw wrapped string after disabling events to prevent recursion
        handles = ax.figure.canvas.callbacks.callbacks[event.name]
        ax.figure.canvas.callbacks.callbacks[event.name] = {}
        ax.figure.canvas.draw()
        ax.figure.canvas.callbacks.callbacks[event.name] = handles

    ax.figure.canvas.mpl_connect('draw_event', _wrap)

def _splitText(text):
    """ Splits a string into its underlying chucks for wordwrapping.  This
        mostly relies on the textwrap library but has some additional logic to
        avoid splitting latex/mathtext segments.
    """
    import textwrap
    import re
    math_re = re.compile(r'(?<!\\)\$')
    textWrapper = textwrap.TextWrapper()

    if len(math_re.findall(text)) <= 1:
        return textWrapper._split(text)
    else:
        chunks = []
        for n, segment in enumerate(math_re.split(text)):
            if segment and (n % 2):
                # Mathtext
                chunks.append('${}$'.format(segment))
            else:
                chunks += textWrapper._split(segment)
        return chunks

def textBox(text, axes, ha='left', fontsize=12, margin=None, frame=True, **kwargs):
    """ Converts an axes to a text box by removing its ticks and creating a
        wrapped annotation.
    """
    if margin is None:
        margin = 6 if frame else 0
    axes.set_xticks([])
    axes.set_yticks([])
    axes.set_frame_on(frame)

    an = axes.annotate(text, fontsize=fontsize, xy=({'left':0, 'right':1, 'center':0.5}[ha], 1), ha=ha, va='top',
                       xytext=(margin, -margin), xycoords='axes fraction', textcoords='offset points', **kwargs)
    wrapText(an, margin=margin)
    return an

用法：

ax = plot.plt.figure(figsize=(6, 6)).add_subplot(111)
an = ax.annotate(t, fontsize=12, xy=(0.5, 1), ha='center', va='top', xytext=(0, -6),
                 xycoords='axes fraction', textcoords='offset points')
wrapText(an)

我删除了一些对我来说不那么重要的功能。调整大小将失败，因为每次调用 _wrap() 都会在字符串中插入额外的换行符，但无法删除它们。这可以通过去除 _wrap 函数中的所有 \n 字符来解决，或者将原始字符串存储在某处并在换行之间“重置”文本实例。

Answer 3

通过在创建文本框时设置wrap = True，如下例所示。这可能会产生预期的效果。

plt.text(5, 5, t, ha='right', rotation=-15, wrap=True)